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Common Canine Intestinal Parasites

Intestinal Worms in Dogs and Puppies

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All dogs are susceptible to intestinal parasites, but some dogs are more vulnerable than others. Read about the four most common types of intestinal worms seen in dogs and how to treat infected dogs. Also learn how some of these parasites may pose a risk to humans as well.

Your veterinarian is the best resource for the diagnosis, treatment and prevention of these parasites. Remember that routine vet visits are key to keeping your dog healthy. Always be sure to communicate with your vet and report any signs of illness as soon as possible.

Roundworms

Canine Roundworm - Toxocara canis
Joel Mills/Wikimedia Commons

Roundworms (Toxocara canis, Toxascaris leonina) are the most common types of intestinal parasites seen in dogs and are especially common in puppies. Adult roundworms live in the intestinal tracts of their hosts, consuming that host's food. The adult roundworm is round, white to light brown in color, and several inches long. These worms are often said to resemble spaghetti.

Adult dogs get roundworms from ingesting roundworm larvae, usually from contaminated soil or infected prey (such as a mouse or other small mammal). Many puppies are born with roundworms after contracting them from their mother's uterus during gestation. Nursing puppies may ingest roundworm larvae in their mothers' milk. Once ingested, larvae make their way to the dog's liver. While developing into adult worms, they travel to the lungs, are coughed up by the dog and then swallowed. The adult roundworms live in the dog's intestines. Their eggs are shed in the dog's stool and develop into larvae. The life-cycle is repeated.

Symptoms of roundworm infection include diarrhea, vomiting, pot-bellied appearance, coughing (dogs may cough up or vomit worms), weight loss and dull hair coat. Many dogs will show no signs of infection at first.

Diagnosis: Roundworms can be diagnosed by your veterinarian after collecting a stool sample and running a lab test called a fecal flotation. The roundworm eggs will typically be seen microscopically in the stool if adult roundworms are present in the small intestine.

Treatment of roundworms involves multiple oral doses of a deworming medication. Deworming only kills the worms in the intestinal tract, so repeated doses are necessary to kill newly developing adult worms. Because puppies are so commonly affected, they are routinely dewormed (whether or not eggs are seen microscopically) during ther first few sets of puppy vaccines. Be aware that not all over-the-counter dewormers are effective. Your veterinarian is the best source for this medication. Note: several types of heartworm prevention also protect against roundworms.

Zoonosis information: Humans can contract roundworms through contact with contaminated soil, potentially leading to a serious condition called Visceral Larva Migrans. Always wear gloves when handling any soil, especially that which may have come in contact with dog feces. Children are at an especially high risk.

Hookworms

Canine Hookworms - Ancylostoma caninum
Joel Mills/CDC/Wikimedia Commons
Hookworms (Ancylostoma caninum, Ancylostoma braziliense) are another relatively common type of intestinal parasites affecting dogs and puppies. The hookworm attaches itself to the intestinal mucosa of its host with its sharp teeth and sucks the host's blood for sustenance. Hookworms are significantly smaller than roundworms and not usually seen in the stool or vomit.

 

Adult dogs get hookworms from contact with contaminated soil that contains hookworm larvae. The larvae may enter the dog by burrowing through the skin or feet when a dog is lying on the ground. Or, the dog may ingest the larvae after contact with contaminated soil, often when grooming. As with roundworms, nursing puppies may ingest hookworm larvae in their mothers' milk. Many hookworm larvae develop into adult worms in the small intestine, but some travel to the lungs, become coughed up by the dog and then swallowed (similar to roundworms). The adult hookworms live and mate in the dog's small intestine. Their eggs are released into the environment via the dog's stool. The hookworm eggs develop into larvae and live in the soil. The life-cycle is repeated.

Symptoms of hookworm infection include pale mucus membranes and weakness (due to anemia). Some animals will have diarrhea and/or weight loss. Many dogs will show no signs of infection at first. Be aware that hookworm infection can be very dangerous to young puppies due to the amount of blood loss that can occur.

Diagnosis: Hookworms can be diagnosed by your veterinarian after collecting a stool sample and running a lab test called a fecal flotation (as with roundworms). The hookworm eggs will typically be seen microscopically if adult hookworms are present in the small intestine.

Treatment of hookworms is similar to that of roundworms. Multiple oral doses of a deworming medication must be given, since the dewormer can only kill worms in the intestinal tract. The dewormer routinely given during puppy vaccines also treats for hookworms. Not all over-the-counter dewormers are effective, so ask your veterinarian about the right medication. Note: several types of heartworm prevention also protect against hookworms.

Zoonosis information: Humans can contract hookworms through contact with contaminated soil. Hookworm larvae can penetrate the skin, potentially leading to a relatively minor but rather uncomfortable condition called Cutaneous Larva Migrans. Avoid walking barefoot in areas where pets may have once defecated (including beaches). Always wear gloves when handling any soil, especially that which may have come in contact with dog feces. Children should not play or sit in areas where pets may have once defecated.

Whipworms

Whipworm - Trichuris
CDC/Wikimedia Commons
Whipworms (Trichuris vulpis) are another type of intestinal parasites commonly affecting dogs. The whipworm lives in the large intestine, where it bites the tissue and embeds its head inside. Like the hookworm, the whipworm sucks the host's blood for sustenance. Whipworms are even smaller than roundworms and rarely seen in the stool. One end of the worm's body is wide wide, while the rest tapers off to a narrow, whip-like head, hence the name "whipworm".

 

Dogs get whipworms from ingesting whipworm eggs that live in the soil (typically ingested through self-grooming). The whipworm eggs pass through the upper GI tract and hatch into larvae in the small intestine. Next, the larvae move down to the cecum or large intestine. There they develop into adult whipworms, living and mating in the dog's cecum or large intestine. Their eggs travel to the environment with the dog's stool. Whipworm eggs can lay dormant in the soil for years until consumed by a new host. Then, the life-cycle is repeated.

Symptoms of whipworm infection may not be present at first. Typically, bloody diarrhea will develop as the infection worsens, possibly leading to chronic bloody diarrhea Anemia is possible, though not as common with whipworm infection as it is with hookworm infection. A whipworm infection can also become severe enough to cause an electrolyte imbalance that mimics Addison's disease.

Diagnosis: Whipworm infection can be difficult to diagnose because whipworms do not lay eggs continuously the way roundworms and hookworms do. Your veterinarian will run a lab test called a fecal flotation (as with roundworms and hookworms). The whipworm eggs may or may not be seen microscopically if adult whipworms are present in the small intestine. A lack of eggs in the stool sample will not definitively rule out whipworm infection. Your veterinarian may recommend repeated fecal testing if whipworms are suspected.

Treatment of whipworms is similar to that of roundworms and hookworms. Multiple doses of a special deworming medication must be given. Over-the-counter dewormers are not effective, so your veterinarian must provide you with the right medication. Because of the long life cycle of the whipworm, treatment is typically repeated months later. Note: Certain types of heartworm prevention also protect against hookworms (specifically: Sentinel and Interceptor, but not Heartgard).

Zoonosis information: Fortunately, the type of whipworm that affects dogs is rarely transmissible to humans. However, precautions should still be taken to prevent contact with dog feces or contaminated soil.

Tapeworms

Canine Tapeworm - Dipylidium caninum
CDC/Wikimedia Commons
Tapeworms (Dipylidium caninum) are intestinal parasites that commonly affect dogs. The are long, flat (tape-like) worms that attach to the small intestine of their host. A tapeworm body is several inches long but consists of multiple segments that grow onto the head and neck of the worm. Each segment has its own reproductive tract.

 

Dogs get tapeworms from ingesting fleas. When flea egss hatch, they consume flea dirt and debris. If present, they will also consume tapeworm eggs. The larval fleas develop into adults as the tapeworm eggs develop inside the fleas. Adult fleas jump on a host (usually a dog or cat). The host chews itself and consumes the adult flea, then the developing tapeworm is released into the host. The young tapeworm attached to the small intestine and grows segments. The end segments are basically egg sacs which eventually detach and make their way out of the host's rectum into the environment. The tapeworm segment, which resembles a grain of rice, breaks open and the eggs are released. If flea eggs are also present in the environment, the life-cycle is repeated. Therefore, tapeworms are only passed from pet to pet by way of fleas.

Symptoms: Tapeworm infection does not tend to adversely affect dogs.

Diagnosis: Tapeworm infection is typically diagnosed after the flat, rice-like segments are seen around the anus or the pet. Tapeworm eggs rarely appear microscopically when fecal flotations are run.

Treatment of tapeworms involves one or more doses of a special deworming medication. Over-the-counter dewormers are not effective, nor are the same dewormers that cure whipworms, hookworms or roundworms. Your veterinarian must provide you with the right medication. Because tapeworms are transmitted via fleas, the only way to prevent re-infection is to eradicate fleas. Deworming may need to be repeated while you try to control fleas. Use of a monthly flea prevention is recommended.

Zoonosis information: Fortunately, the type of tapeworm that affects dogs is not directly transmissible to humans. However, tapeworm infection can be transmitted to humans by accidental ingestion of a flea.

NOTE: there is another type of tapeworm that can affect pets: Taenia. This type of infection is less common and contracted after a pet consumes an intermediate host such as a rabbit or mouse. Fortunately, this type of tapeworm does not tend to have an adverse affect on the host. In addition, the same medication that kills Dipylidium caninum also kills Taenia.

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